PURPOSE: To correctly decide a portion to be worked without lowering the work efficiency of cutting by notching a notch portion extended from the outer periphery of a plate piece as a work piece formed by gullet cutting to the finish line.

CONSTITUTION: At least a portion of a cutting line at the time of cutting process, cutting is performed outside the finish line A of a plate piece 2 as a work piece. Subsequently, a notch portion 3 extended from the outer periphery of the plate piece 2 as a work piece formed by gullet cutting to the finish line A is notched. The base portion A of a notch portion 3 which is formed by the notch cutting process and correctly alinged with the finish line A is taken as a starting point, and a portion to be worked subsequently is specified. Thus, a portion to be worked can be decided correctly without lowering the work efficiency of cutting so as to improve the dimensional accuracy for working and the productivity.